718 Proceedings. 



clear conception as to the progress and development of life on the earth, 

 it may be well if I refer briefly to the theories which have been set up 

 as to the origin of this earth of ours. Kant, Laplace, and Herschel (W.) 

 explained the harmony prevailing in what is known as the solar system 

 by premising that at one period an original nebula existed, of which 

 the remains at the present time are the sun and the several planetary 

 bodies, with their satellites. This nebula was diffused in space at least 

 as far as the farthest member of the system. As it began to condense 

 towards a centre interspaces of matter were left behind, and these, in 

 their turn, continued to condense by the dispersion of their heat, and 

 thus the planets grew. Whilst it is difficult to explain by the nebular 

 theory, as this system is called, the cause of the condensation of 

 materials composing the nebula about special centres, it is possible to 

 explain the sequence of materials which might be said to form the 

 earth's crust or envelope. Thus the air surrounds the earth, then 

 come the water and surface rocks, and these are severally much 

 lighter specifically than the average density of the earth. As we know 

 it the earth is round, spheroidal as to shape, and consists of land and 

 water with an aerial envelope. It is usual to say that the land is only 

 about one-fourth of the earth; but this is true only so far as the sur- 

 face is concerned, the proportion of water- to land - surface being as 

 145 is to 52. But the actual quantity of water, after all, is very small 

 when the land and water, bulk for bulk, are compared. The average 

 depth of the entire ocean is said to be about 12,000ft., whilst the average 

 height of the land is not more than 2,500ft. The quantity of water 

 upon the earth at the present time is sufficient to cover the entire 

 surface to a depth of nearly 8,000ft., or, say, a mile and a half. As 

 a frozen mass it would cover the earth to a depth of nearly 9,000ft. 

 A cubic foot of water percolating through the land would not, I esti- 

 mate, be traceable to a depth of 100ft., the effect being the same as 

 if a cubic inch of water were distributed over a square surface of lOOin. 

 with a depth of lin. Thus, if all the waters of the ocean were to be 

 absorbed by the land, then, on the estimate of percolation given above, it 

 would not affect the crust to a depth of more than 150 miles. That 

 the earth's crust absorbs water is certain, and as far as our knowledge 

 goes there is no reason why all the water which occupies so much of 

 the earth's surface as ocean should not pass into the crust and be 

 absorbed by it. Thus the earth might become, simply by the process 

 of absorption, uninhabitable. As far as is known, the materials which 

 form the earth were originally arranged according to their specific 

 gravities ; in fact, it appears to me that a large body like the earth is 

 inconceivable on the supposition that the envelope, or outer covering, 

 is specifically heavier than the materials which such envelope would 

 enclose. The contraction of that part of the original nebula which 

 goes to make up the earth took place through the diffusion of heat into 

 space, and contraction of the earth will proceed until the whole heat now 

 centred in the earth, together with that received from the sun, will 

 be similarly diffused in space. And that this is the order of nature 

 seems probable from the facts which geology and physiography teach 

 as to the structure of the earth and the development of animal and vege- 

 table life. With no degree of certainty can it be said when or in what 

 manner life first appeared on the earth — whether in a hot temperature or 

 a cold one ; but we know that the lovver forms of life must have existed 

 before the higher, and even the vegetable before the animal. The 

 physical conditions were such that no other plan was possible. Experi- 

 ments show that the lowest forms of life, to which reference has already ■ 

 been made, including bacteria andamoebce, cannot even exist in a tempe- 

 rature much below the boiling-point of water, and their potency for harm 

 as fermentative agents is destroyed in temperatures below freezing-point. 



